Perhaps the overriding intellectual imperative of a globalised world, in which no culture can hope to isolate itself or to avoid the encounter with others, is to make it possible for those holding different and potentially antagonistic beliefs to live in peace with one another. This is a particular duty for those whose vocation it is to teach with authority, whether sacerdotal or academic; yet it is a duty that is almost always shirked. For priests and professors alike are at home with the formulation of doctrine, the exegesis of texts and the preservation of tradition. They are temperamentally unsuited to the confrontation between theory and practice. Taking responsibility not only for what is taught but for what follows from the teaching, for what is done in the name of religion or ideology, seems to pose an almost insuperable challenge for the guardians of doctrine.

Yet doctrine, “teaching” or “that which is taught”, implies, like the cognate term “doctor”, worldly as well as spiritual authority. When the University of Oxford awards degrees, the Vice-Chancellor and his Proctors address the new graduate as Domine or Magister (“lord” or “master”). Popes are symbolised by (and until St John XXIII regularly wore) a triple crown, indicating their teaching authority, their Magisterium, over secular rulers; “Professor” takes precedence over other titles, even inherited ones; “Rabbi” carries a similar prestige. Those entitled to teach on behalf of a religion wield a unique kind of authority and their influence may be political no less than spiritual.

How then may the arbiters and exponents of doctrine be persuaded to soften their orthodoxy sufficiently to open up a space in which competing claims to truth may be resolved or not, as the case may be, but in any case without bloodshed? The greatest religious thinkers may range freely across an intellectual terrain they have made their own, but lesser minds tend to stick rigidly to rules and to the literal interpretation of scripture. The deadening effects of the latter are the reason why terms such as “doctrinaire” and “dogmatic” have acquired such negative significance. It is sometimes the case that the doctrinaire and the dogmatic elements within a faith community restrict, censor or even excommunicate the freer, more creative spirits. But it is also true that when the doctrines of the free spirit depart too radically from orthodoxy, perhaps in the attempt to achieve ecumenical goals, then the charge of heresy may indeed be justified and a parting of the ways becomes inevitable. The new doctrine either dies with its originator, or becomes the seed of a new religion. The distinctions between Sunni and Shiite, or between Catholic and Protestant, may have grown more entrenched over the centuries, but at their origins were genuine theological disputes. The Inquisition’s most notorious case, against Galileo, was not against his discoveries but his adherence to a theory, Copernican heliocentrism, which not even the greatest of contemporary astronomers, Tycho Brahe, had been able to test to his satisfaction. One may deplore the anathematisation of Spinoza by the Amsterdam Jewish community, but his critiques of Biblical and Halachic authority were indubitably heterodox. In all these cases, the forces of change were resisted by the religious establishment on perfectly rational grounds. We must not expect anything to be different today — except that secular establishments are apt to be at least as protective of their ideological purity as religious ones are of doctrinal orthodoxy.

The time-honoured method by which antagonistic doctrines may be obliged to acknowledge one another is dialogue. Already in the Middle Ages we hear of disputations between representatives of the world religions at the courts of Mongol khans and other oriental potentates. But ecumenical encounters are evidently older than that. There are examples of them throughout the Hebrew Bible. The New Testament accounts of the interrogation of Jesus by Pontius Pilate show that pagans and Jews were accustomed to hold religious dialogues even in the most improbable circumstances.

It is worth dwelling on that particular dialogue, in the version handed down by St John’s Gospel, because it anticipates so many of today’s problems. Pilate asks Jesus: “Art thou a King then?” Jesus answers: “Thou sayest that I am a King. To this end was I born, and for this cause came I into the world, that I should bear witness unto the truth: every one that is of the truth heareth my voice.” Pilate replies with a question: “What is truth?” But he does not wait for an answer.

Now, every religion makes strong claims to truth — not merely a truth but the truth. For this reason, no religion can be comfortable with epistemological relativism. In 2002, the then Chief Rabbi Jonathan (now Lord) Sacks published The Dignity of Difference, subtitled How to avoid the Clash of Civilisations, in which he sought to establish a framework for different faiths to live alongside one another and engage in dialogue, while acknowledging that their rival truth claims could not be reconciled. However, his fellow Orthodox rabbis were unhappy with some of the book’s formulations, which in their view went too far and could be interpreted as relativising the truth claims of Judaism. Sacks agreed to rewrite an entire chapter to meet their concerns. For example, in the first edition we read: “[Judaism] believes in one God, but not in one religion, one culture, one truth. The God of Abraham is the God of all mankind, but the faith of Abraham is not the faith of all mankind.” In the second edition, this has been changed to: “[Judaism] believes in one God but not in one exclusive path to salvation. The God of the Israelites is the God of all mankind, but the demands that are made of the Israelites are not made of all mankind.”

Sacks claimed that, for Jews, there was nothing controversial in his main argument — that the Abrahamic monotheisms of Judaism, Christianity and Islam have a theological basis for mutual respect, based not on relativism but on the common concept of covenant. Evidently, though, the notion that Jews do not believe in one universal truth was highly controversial. The fact that Judaism does not claim exclusivity in seeking salvation does not mean that its truth claims are not absolute.

It has become impolite, even taboo, to point out the incompatibility of such religious truth claims. In a recent column, the Catholic writer Piers Paul Read criticised an American Jewish friend who had rewritten in Hebrew the Latin texts of the B Minor Mass to produce “the Jewish Bach”. The fact that this project made him feel “profoundly uneasy” implied, wrote Read, that he was not truly ecumenical. While acknowledging the decrees of the Second Vatican Council, enjoining Catholics to treat “our older brothers in the faith” with respect, Read is dismayed by the Jewish rejection of Jesus. He suspects that “were I not a Catholic, I would not believe in God”. Quoting Blaise Pascal, Read accepts that “true Christians and true Jews have only one religion”, but that does not resolve the stark choice: either Jesus Christ is the Messiah, or he is not. For him “the question to be answered is whether what [religions] teach is true and, like Pascal, the only God I can believe in is the God foretold by the Jewish prophets and revealed by Christ.”

I find Read’s frankness refreshing, although I suspect that he and Rabbi Sacks would in practice find a great deal in common. Catholics and Jews, at any rate if they are orthodox, both take doctrine, prayer and ritual seriously; they have survived for so long precisely because they maintain unambiguous criteria for membership. It is, indeed, the clear demarcation between these two orthodoxies that has helped to make dialogue between them so fruitful. The documents Lumen Gentium and Nostra Aetate, issued by the Second Vatican Council half a century ago, were the product of decades of dialogue between Catholic theologians, several of them converts from Judaism, and Jews, including the Holocaust survivor Jules Isaac, who made an impassioned appeal to Pope John XXIII at an audience in 1960 to abandon the teaching of contempt for the “blindness” of Jews.

The language of these documents was fiercely fought over at the Council and repays close reading. Of the Jews Lumen Gentium says that “this people remains most dear to God, for God does not repent of the gifts he makes nor of the calls he issues”, a direct quotation from Romans 11:29. Lumen Gentium goes on to acknowledge that “the plan of salvation also includes those who acknowledge the Creator . . . Nor does Divine Providence deny the helps necessary for salvation to those who, without blame on their part, have not yet arrived at an explicit knowledge of God”. In other words, the council abrogated the Augustinian dictum: Salus extra ecclesiam non est (“there is no salvation outside the Church”). In Nostra Aetate, the council fathers went further, explicitly condemning “hatred, persecutions, displays of anti-Semitism directed against Jews at any time and by anyone”. They abandoned the ancient accusation of deicide “against all the Jews, without distinction, then alive, nor against the Jews of today . . . the Jews should not be presented as rejected or accursed by God, as if this followed from the Holy Scriptures.” As John Connelly points out in his book From Enemy to Brother, the German Cardinal Bea, who oversaw the drafting of Nostra Aetate, had advocated precisely these ideas until the early 1960s: “Cardinal Bea found a new language to talk about Jews only after he began talking to Jews.” Doctrine and dialogue exist in a delicate symbiosis.

Not surprisingly, these declarations and others like them since have not been universally popular among some Christians, who cling to “supersessionist” interpretations of the New Testament. Others are hostile to the State of Israel, identifying the Church with the Palestinian cause while ignoring the global persecution of Christians by Islam. The Vatican has not been immune to such attitudes, yet successive popes, beginning with John XXIII but especially the Polish, German and Argentine Popes John Paul II, Benedict XVI and Francis, have taken great care to maintain and expand Judaeo-Christian dialogue.

What we have not seen, however, is any sustained attempt to deepen the exegesis of the key text for Catholic-Jewish theology: St Paul’s Epistle to the Romans, especially chapters nine to 11. As we have seen, the council fathers drew on Paul’s language, but the deepest question remains unresolved: that of salvation. Paul writes in Romans 11:25-26: “For I would not, brethren, that ye should be ignorant of this mystery, lest ye should be wise in your own conceits; that blindness in part is happened to Israel, until the fullness of the Gentiles be come in. And so all Israel shall be saved.” Paul appears to be prophesying that the Jews “in part” have been ordained to remain outside the elect until the Church has accomplished its mission to the Gentiles, but that nevertheless God is bound to keep his promise that the Jewish people as a whole, converted or not, will ultimately attain salvation.

Paul — himself a Jew, a Roman citizen, and the apostle of the Gentiles — implies that the distinction between Jew and non-Jew will disappear at the end of time — but not before. “I say then, Hath God cast away his people? God forbid. For I also am an Israelite, of the seed of Abraham, of the tribe of Benjamin . . . For if the casting away of them [Israel] be the reconciling of the world, what shall the receiving of them be, but life from the dead?” The Jews, in the New Testament, are still God’s means to save all mankind — just as they always were in the Hebrew Bible. The Jewish rejection of the Gospel has not altered their providential function, nor their prospect of redemption.

In grappling with this Pauline doctrine, two great German-speaking Jesuit theologians, Karl Rahner and Hans Urs von Balthasar, have contributed important but contrasting ideas. To Rahner we owe the idea of the “anonymous Christian”, the person outside the Church who by God’s grace attains salvation through following the dictates of his conscience. As we have seen, the Second Vatican Council implicitly adopted this idea of “inclusivism”, stating in Gaudium et Spes that “the Holy Spirit in a manner known only to God offers to every man the possibility of being associated with this paschal mystery”. Balthasar, however, is sceptical about what he calls “a superficial ecumenism”. He rejects the notion of “an invisible church which would be the true Catholic church permeating all confessions, and a visible church which is just one of many variants of being Christian”. However, for Balthasar even those who have turned away from God are not wholly beyond hope — because Christ has been there before them, having descended into hell after his crucifixion. “Even what we call ‘hell’ is, although it is the place of desolation, always still a Christological place.” Balthasar spent many years in dialogue with the great Jewish sage Martin Buber, and his struggle to make sense of the Epistle to the Romans influenced his entire theology of history. God’s mercy, Paul tells us, embraces the whole Jewish people, not just the “remnant” who converted to Christianity. And this insuperable fact of the universality of God’s mercy led Balthasar towards his most controversial teaching: that humanity as a whole, Jews and Gentiles, will ultimately be saved — that hell, in other words, is empty.

This doctrine of universal salvation finds resistance in Western Christianity, with its emphasis on free will and responsibility, but the hope that all shall be saved is an old one, expressed by the Greek Orthodox concept of apokatastasis, the eschatological “restitution” of all things. This is close to the Jewish notion of tikkun olam, or “healing the world”. Rahner’s doctrine of the anonymous Christian and Balthasar’s doctrine of universal salvation offer contrasting but compatible solutions to the problem with which we began: the problem of truth.

Each of the last three popes has had Jewish interlocutors and friends among the rabbinate, but none has been closer than the relationship between Pope Francis and Rabbi Abraham Skorka. Francis, according to Skorka, “feels us [Jews] to be at the root of his belief”. The two Argentines have found enough common spiritual ground to be able to live with the competing truth claims of their respective religions. Each of them, the Jesuit and the Jew, is confident that they are on the same side. Doctrinal orthodoxy matters, for without it neither would be sure enough of his own ground to be able to step onto the other’s. But doctrine is not all that matters. There is a truth that respects and transcends doctrinal differences, the truth that Paul sought to articulate in his paean of praise to the Jewish people in Romans 9:4: “To them pertaineth the adoption, and the glory, and the covenants, and the giving of the law, and the service of God, and the promises . . .” No Christian ought ever to speak to or about Jews without such respect, never forgetting that Jesus was Jewish not only in flesh and blood but in his teaching. The imitation of Christ is therefore, in some unfathomable but deeply significant sense, the act of drawing closer to and identifying with the Jewish people.

We have seen how doctrinal differences may sometimes develop through dialogue to the point where they are transcended by a higher order of truth. The theological issues that provoked the Reformation — justification by faith alone, purgatory and predestination, the priesthood of all believers — all turned on the interpretation of Pauline Scripture. None is now seen as an insuperable stumbling block by most Protestant or Catholic theologians. The question of salvation is central here, too: neither side now sees damnation as the price of error. These doctrinal differences have been transcended by ecumenical dialogue, stimulated by the mutual respect due to those martyred by the Nazis such as Dietrich Bonhoeffer and Edith Stein, to the point where five years ago a German Pope, Benedict XVI, could celebrate Martin Luther at the reformer’s Augustinian convent in Erfurt.

So there are parallels with the Catholic-Jewish relationship. Such doctrinal differences have, however, been superseded by new truth claims: in the case of Protestants and Catholics, by sharply different attitudes to sex and the family or to the role of women in the Church; in the case of Jews and Christians, disputes over Israel and the Palestinians. These arguments are no longer about who is to be saved and who damned in the next world, but who is to be damned in this one.

Above all, we cannot leave Islam out of account. Whereas dialogue between Catholics, other Christians and Jews is generally conducted in a civilised way, attempts to reach out to the Muslim world have often been rebuffed. This is not for want of trying. Pope John Paul II visited the Umayyad Mosque in Damascus, an ancient centre of Sunni Islam, in May 2001, and kissed the Koran — something that would once have been unthinkable. Four months later came 9/11. Then in 2006 Benedict XVI gave his Regensburg lecture, which quoted the Byzantine Emperor Manuel II Paleologus condemning Muhammad for imposing Islam by force. An unfortunate translation rendered the sentence thus: “Show me just what Muhammad brought that was new, and there you will find only things evil and inhuman, such as his command to spread by the sword the faith that he preached.” Even though the Pope had declared the Emperor’s formulation “unacceptable” and the words “evil and inhuman” were swiftly corrected to “bad and inhumane”, the reaction across the Muslim world was one of violence, not least against priests and nuns. The Pope’s apology was not accepted by many Muslim authorities, but later there were overtures from Islamic clerics which have opened up the possibility of dialogue. When Benedict visited Turkey, he called for “authentic dialogue between Christians and Muslims, based on truth and inspired by a sincere wish to know one another better, respecting differences and recognising what we have in common.” Pope Francis has continued the quest for authentic dialogue, but so far there has been little or no willingness by Muslim leaders to promote reciprocity of religious freedom. Under Islam, Jews and Christians continue to suffer legal discrimination, violent persecution and even genocide.

As long as truth is sought by the light of reason, doctrinal commitments and differences do not preclude dialogue between religions. Violence, however, renders impossible what Martin Buber called the Ich-Du (“I-Thou”) relationship — a relationship that sees the image of God in every human being. The revealed truth that Jews and Christians in their different ways express in doctrine and practice is enriched by dialogue, because in the human encounter with the other faith we also catch glimpses of the divine encounter we all seek. Reaching out to Muslims is an imperative for Jews and Christians only in the absence of violence. Mutual respect requires mutual toleration; religious reciprocity is not a favour but a right. The only consolation is that persecution has drawn Jews and Christians closer than ever before. As the Prophet Amos says, “Can two walk together, except they be agreed?” Jews and Christians should at least agree on this: that we like to walk together — so much, indeed, that we will never again be parted.